In a computer disc drive, data is stored on discs in concentric tracks. In disc drives with relatively high track densities, a servo feedback loop is used to maintain a head over the desired track during read or write operations. This is accomplished by utilizing prerecorded servo information either on a dedicated servo disc or on sectors that are interspersed along a disc. During track following, the servo information sensed by the head is demodulated to generate a position error signal (PES) which provides an indication of the distance between the head and the track center. The PES is then converted into an actuator control signal, which is used to control an actuator that positions the head.
Misalignment of the read/write heads with respect to the tracks causes increases in read/write errors and a slowdown in read or write operations. Accurate positioning of read/write heads is required even in the presence of anomalies such as aging, temperature changes, changes in orientation of the disc drive, humidity, shock and vibration.
Current servo control systems are usually designed with parameters which are set at the time of system design to be the most acceptable compromise for all operating conditions including the above mentioned anomalies. Using system parameters set at the time of design or manufacture limits the servo loop's performance under changing conditions. In addition, due to the variations inherent to the manufacturing process, different drives (even different heads in one drive) may be significantly different. Thus, disc drive servo control systems using fixed parameters do not function optimally under different operating conditions. These problems worsen as track densities increase.
The present invention addresses these problems and offers other advantages over the prior art.